242 



258. P. muticum Kiitz. 

 Var. longicorne Rac. 



1. c. tab. II, fig. 18, 19. 



From a watercourse on Kirkebokamp near Thorshavn (Str.); and 

 in Plankton from Sorvaagsvatn (Vaago). 



259. P. Tetras (Ehrenb.) Ralfs. 

 Lagerh. Pediastr. p. 54. 

 Kvalbo Ej de (Syd.). 



260. Coelastrum sphæricum Nagl. 



In Plankton from Sandsvatn (San do). 



261. C. cubicum Nagl. 

 Grothusvatn (Sand 6). 



262. C. microporum Nagl. 



Viderejde (Vid.); Skopen and Grothusvatn (Sand o); in Plankton 

 from the large lake near Ejde (Ost). 



Order XVI. ULVACEÆ. 



263. Prasiola crispa (Lightf.) Menegh. Plate IX, fig. 2. 



Is very common especially on damp grass roofs where it occurs 

 in large green curly patches. It has been already found by Lyngbye 

 (Hydrophyt. p. 32, tab. 6), his Ulva terrestris, as the specimens in 

 his herbarium show, is this species. As is well-Iaiown, Hormidiiim 

 nuirale (Ag.) Kiitz. is a phase of developement of this species and 

 also in the material from Thorshavn specimens were found in 

 different stages of development, from Hormidiiim miirale to fully 

 developed Prasiola. I have given a figure of such a young Prasiola 

 (Plate IX, fig. 2). The base consists of some rhizoid-like branches, 

 containing thick-walled cells, the branches more or less grown to- 

 gether so as to form a small disc with which the plant is attached. 

 Just above this »attachment-disc« follows a short Hormidiiim-Vike 

 part formed of a single row of cells; after a slight constriction, the 

 filament expands inconsiderably, now consisting of one stratum of 

 cells, this slightly broader part — as yet quite a narrow band — 

 which is of some length and bears rhizoids here and there, finally 

 broadens and takes the character of Prasiola^. 



Hormidiiim murede has also been found by Lyngbye (Hydro- 

 phyt. p. 95) as the Oscillatoria miiralis mentioned by him, judging 



' Cfr. Imhåuser: Entwicklungsgeschichte und Formenkreis von Prasiola«. 

 (Flora 47. 1889). 



